An axial flow fan may be used to produce a flow of cooling air through the engine compartment of a vehicle. For example, an airflow generator used in an automotive cooling application may include an axial flow fan for moving cooling air through an air-to-liquid heat exchanger such as an engine radiator, condenser, intercooler, or combination thereof. The required flow rate of air through the fan and change in pressure across the fan vary depending upon the particular cooling application. For example, different vehicle types or engine models may have different airflow requirements, and an engine radiator may have different requirements than an air conditioner.
To provide adequate cooling, a fan should have performance characteristics which meet the flow rate and pressure rise requirements of the particular automotive application. For example, some applications impose low flow rate and high pressure rise requirements while other applications impose high flow rate and low pressure rise requirements. The fan must also meet the dimensional constraints imposed by the automotive engine environment, which is typically non-ducted. Known fans which meet such aerodynamic requirements and dimensional constraints typically have relatively high solidity values and weight.
Critical performance characteristics of a fan can be represented by two curves, a static pressure curve and an efficiency curve. A static pressure curve is obtained by plotting the static pressure across the fan as a function of the volume flow rate through the fan. Generally, the static pressure curve of known fans can be approximated by a second or third order equation with a predominantly negative slope. The maximum pressure rise occurs at a low flow rate and the minimum pressure at a high flow rate.
The efficiency curve plots the static fan efficiency as a function of the volume flow rate through the fan. Generally, the curve of known fans can be approximated by a second order equation with a local maximum. Typically the local maximum forms a relatively sharp peak at an intermediate flow rate. The narrow range of volume flow rate over which peak efficiency is maintained limits the range of automotive applications that can be served compared to a fan with a similar peak value of efficiency but having a broad and flat efficiency curve.
Accordingly, it would be desirable to provide an improved fan for moving air with high efficiency, low solidity and low weight. It would also be desirable to provide an axial flow fan having low solidity and low weight which has performance characteristics meeting the requirements imposed by various automotive applications. Further, it would be desirable to provide an axial flow fan having a relatively broad and flat efficiency curve. In addition, it would be desirable to provide a fan capable of covering a broad range of automotive applications.